In 2015, the authorities in California documented 837 hate-crime incidents, charting a surge in offenses motivated by religious intolerance toward Muslims and Jews, while crimes against Latinos grew by 35 percent.

Last week, shortly after Donald J. Trump was elected the country’s next president, the Southern Poverty Law Center put up a form on its website encouraging people to share details about potential hate crimes. By the next day, they’d received about 250 reports – more than they’re used to seeing in six months.

Then on Monday, the FBI released its latest national tabulation of hate crimes, data that showed an overall uptick of 6.8 percent from 2014 to 2015. The accounting, drawn from information passed on to the bureau by state and local law enforcement agencies, charted a 67-percent increase in anti-Muslim hate crimes.

The mix of information – state level, anecdotal, federally collected, dating from two years ago to last week – is sure to fuel the country’s evolving conversation and concern about the potential for violence in a divided America. Already, those worried about the consequences of Trump’s triumph have seized on some of the reports to stoke worry about emboldened white nationalists. And Trump’s supporters have moved quickly to try and debunk the swirl of alleged incidents of intimidation and violence that have surfaced in social media.

But even in the early stages of what promises to be a prolonged focus on crimes colored by prejudice and politics, there appears to be one irrefutable truth: the data is deeply flawed.

James Comey, the director of the FBI, said as much even as he announced the bureau’s latest batch of numbers.

“We need to do a better job of tracking and reporting hate crimes to fully understand what is happening in our communities and how to stop it,” Comey said.

More than 3,000 state and local law enforcement agencies don’t report hate crimes to the FBI as part of its annual national survey of crime in America. Professor Brian Levin, who heads the Center for the Study of Hate and Extremism at California State University, San Bernardino, said the entire state of Hawaii fails to file any such reports.

And many of the law enforcement agencies that do choose to participate do not appear to be particularly rigorous about documenting hate crimes and passing that information onto the federal authorities.

“A lot of agencies just submit a piece of paper saying they had no hate crimes,” added Levin, noting that the vast majority of police and sheriff’s departments reported no hate crimes last year.

The data appears particularly spotty in much of the South, a region with a long history of racial strife. Police in Mississippi reported zero hate crimes in 2015. In Arkansas, the number was eight. In Alabama, it was 12.

It seems the number of hate crimes on college campuses is also undercounted by the FBI. The most recent statistics gathered by the U.S. Department of Education appear to show at least twice as many offenses occurring at colleges and universities as the FBI data.

The FBI “data system is of little help to authorities who investigate and track hate crimes,” wrote Ronald L. Davis, head of the Justice Department’s Office of Community Oriented Policing Services, in an essay published earlier this year. “This is a significant problem because, if the authorities do not know how many hate crimes are committed, they cannot get an accurate picture of whether hate crime laws are effective, which can lead to fewer resources allocated to combatting hate crimes.”

An FBI spokesperson acknowledged that nearly 20 percent of law enforcement agencies don’t participate in the program, but said the bureau was working “to improve the data collection.”

A key problem, said Phyllis Gerstenfeld, author of a well-known book on hate crimes, is that the FBI has no legal mechanism to compel law enforcement agencies to file crime reports or ensure that they submit accurate information.

Still, some states are doing an admirable job, noted Gerstenfeld, a criminology professor at California State University, Stanislaus. In California, for example, police officers receive training on hate crimes as part of their initial education at the police academy, which can help officers identify bigotry-driven offenses. California law requires police and sheriff’s deputies to closely monitor hate crimes and share their findings with both the California Attorney General and the FBI.

In total, the FBI documented 5,850 hate-crime incidents in the report it issued Monday, most targeting people on the basis of race or ethnicity, religious affiliation or sexual orientation. For some, the surge in crimes against Muslims was not surprising.

“It confirms what we’ve been seeing on the ground since late last year – a spike in hate crimes against Muslims,” said Ibrahim Hooper, communications director for the Council on American-Islamic Relations, an advocacy group.

Since Trump claimed the presidency on Nov. 8, social media has been deluged with first-person accounts of racist incidents and attacks on Muslims, prompting BuzzFeed to compile a listicle titled “Here Are 26 Reported Racist Incidents After Donald Trump’s Victory.” This catalog of abuse included graffiti (lots of swastikas, and, in upstate New York, an exhortation to “Make America White Again”); violence (an African-American college student assaulted in Ohio); and intimidation in myriad forms (black students receiving online invitations to a lynching in Pennsylvania, a Muslim woman who was told “Your time’s up, girlie” on the New York subway, etc.).

Oren Segal, the director of the Anti-Defamation League’s Center on Extremism, believes it’s too early to tell if reports are higher than normal because incidents are happening more frequently or because people are simply more aware of them. But he said the direct connection to a single politician is unique. “The fact that so much of it is being linked to our presidential campaign is very, very disturbing,” he said.